Allergic contact dermatitis (ACD) is caused by extended contact with a sensitizing substance. It is a pruritic dermatitis characterized, during the acute phase, by red patches that are often infiltrated and edematous, and with soft and poorly defined edges.

To date, more than 3,000 chemicals have been described that can cause an allergic skin reaction. The most common allergenic agents are metals, perfumes, cosmetics, dyes and gums.

To diagnose a contact allergy, the patch-test is used. The test is performed by applying strips (patches)  containing the suspect substances to the patient’s skin (usually on the upper back). The patches are removed after two or three days.